Natural resources such as gas, oil, and water residing in a subterranean formation or zone are usually recovered by drilling a wellbore down to the subterranean formation while circulating a drilling fluid in the wellbore. After terminating the circulation of the drilling fluid, a string of pipe, e.g., casing, is run in the wellbore. The drilling fluid is then usually circulated downward through the interior of the pipe and upward through the annulus, which is located between the exterior of the pipe and the walls of the wellbore. Next, primary cementing is typically performed whereby a cement slurry is placed in the annulus and permitted to set into a hard mass (i.e., sheath) to thereby attach the string of pipe to the walls of the wellbore and seal the annulus. Subsequent secondary cementing operations may also be performed.
During the cementing process, a drawback to the use of cement slurries containing high-density additives (e.g., weighting agents) is their high viscosity due to the high solids content, as well as the presence of viscosifying agents (e.g., viscosifying polymers) which function to prevent settling of high density materials. These factors among others often necessitate the use of high pump pressures and/or low pump rates to place the slurries in the wellbore. This issue is often mitigated only slightly by the inclusion of high levels of additives such as dispersants. Addition of dispersants to reduce surface viscosities may also result in settling of solids when the slurries are exposed to the maximum bottom hole temperature due to thermal thinning of the viscosifying polymers. Additionally, the higher viscosity of the cement slurry is often advantageously exploited only after it passes through the deeper end of the casing (“turns the corner”) and contacts the formation where it may function to mitigate fluid loss and settling. Consequently, there is continuing need and interest to develop wellbore cementing compositions (e.g., cement slurries) having desirable rheological and operational properties.